Clinical studies have been undertaken to identify new agents or combinations of agents that may have activity in patients with relapsed acute leukemia. In 12 patients the combination of 5-azacytidine plus pyrazofurin and in 20 patients the single agent VP16-213 in high doses have both been found to be ineffective. AMSA used in 17 patients as a single dose and in 16 patients on a multiple dose schedule and the combination of cytosine arabinoside (ARA-C) plus thymidine (TdR) used in 28 patients both have shown significant antileukemic activity in patients with relapsed ALL and ANLL. The response rates (CR plus PR) in either of the last two studies is in the range of 30%-50%. These studies are continuing and it is still too early to develop stable response data.